A DC-Iris control system is widely used in Security Internet Protocol (IP) cameras. A DC-Iris is a motor-driven, automatically adjustable iris opening that responds to changes in light levels. An analog signal is used to control the iris opening. Circuitry is implemented to convert the analog signal into motor control signals. In a DC-iris lens, the circuit resides inside the camera.
The image quality captured by a camera is dependent on getting the right iris opening (i.e., aperture). A security IP camera is often used in various lighting environments. In order to optimize image quality, a camera needs to have control over the position of the iris opening.
Proportional-Integral-Derivative (PID) control systems are used to control a DC-Iris lens. A proportional coefficient has the effect of reducing the rise time and will reduce, but not eliminate, the steady-state error. An integral coefficient has the effect of eliminating the steady-state error for a constant or step input, but may make the transient response slower. A derivative coefficient has the effect of increasing the stability of the system, reducing the overshoot, and improving the transient response. PID coefficients may be dependent on each other and changing one of these variables can change the effect of the other two.
PID coefficients can be selected to meet a target of reaching set point quickly while reducing overshoot and flicker. These targets also need both good dynamic characteristic and static characteristic of the control system. Conventional PID controllers are unable to meet these targets while having good dynamic characteristics and static characteristics. Furthermore, there are many types of DC-Iris lenses implemented in camera products lines. Each type of DC-Iris needs a specified set of PID control coefficients. If a mismatched DC-Iris lens is mounted, the PID coefficients may not work well. End users and distributors may change a DC-Iris lens for a camera to achieve a desired field of view (FOV) or focus.
It would be desirable to implement a DC-Iris control system.